The present invention relates generally to an improved flexible circuit assembly, and more particularly to an improved flexible circuit with signal traces arranged in stripline cable or microstrip configuration and provided with improved shielding and impedance characteristics. The flexible printed cable, stripline or microstrip devices of the present invention are fabricated in such a way that the finished product is designed or tailored to meet the characteristic impedance requirements of such devices when incorporated into products commonly found in the marketplace.
Flexible printed cables in stripline or microstrip configuration are widely used as interconnects for computer and telecommunication applications. Recently, these applications have required operational capability at higher and higher frequencies. For example, in order to take full advantage of recent advances and improvements in integrated circuit devices, improved packaging schemes are necessary. Current packaging techniques have become a recognized obstacle in being able to take full advantage of the improved capabilities and improved performance of electronic devices. While problems arising through the use of digital circuitry are sometimes different from those arising with analog circuitry, it is generally recognized that both designs are requiring operational capability at more rapid rates, with switching speeds in certain current designs entering the gigahertz range. In order to take full advantage of these technical advances in devices, a requirement arises for the utilization of short leads, shielding, ground planes, as well as certain other features. For example, stripline cable devices prepared in accordance with the present invention provide an integrated ground feature with performance capabilities approximating or equivalent to those of coaxial configuration. The features of the present invention provide a means of achieving reasonably full utilization of recent improvements in device technology, so that products employing modern devices can be expected to deliver high-speed performance while maintaining production costs compatible with those required in the current consumer electronics market. The improved flexible printed cable of the present invention has been found to meet current demands for both shielding and controlled impedance. Devices prepared in accordance with the present invention possess the advantage of having the signal layer disposed in and along the neutral axis, thereby making the product highly useful in applications requiring dynamic flexing. The features of the present invention employ standard single layer flex-circuitry processing technology to achieve or attain two or three layer products, but in addition, provide innovative treatment of the circuitry so as to accommodate novel folding and ultimate assembly so as to interconnect the ground plane and the signal layer. The features of the present invention provide for utilization of these advantages in a variety of circuitry configurations, with particular application to stripline or microstrip configurations.
In addition to the improved control of impedance and improvements in normal flexure performance, the products prepared in accordance with the present invention incorporate one or more slots and bridge arrangements so as to enhance the ability to resist or withstand delamination which may otherwise occur due to buckling of the outer layers following multiple flexure operations. In other words, product prepared in accordance with the present invention has been found to resist the tendency to buckle and form anomalies or zones of delamination as a result of being subject to multiple flexural excursions.
The performance advantages, including electrical as well as mechanical performance advantages are achieved without sacrificing economies of production. In other words, the advantages available in product produced in accordance with the present invention are achieved without undergoing significant increases in unit cost, with the features of the present invention providing a low cost alternative to normal production of three-layer flexible circuits. The printed cable and stripline products of the present invention are designed to be compatible with conventional connectors, including ZIF connectors. While the illustrations provided herein are shown in a ZIF configuration, it will be appreciated that the features of the present invention permit use with other conventional connectors as well. One particular advantage of the arrangement of the present invention is that it makes possible the utilization of a form of shielded cable which is compatible with and utilizes ZIF connectors.